Long gun to sidearm transition is a good skill to learn and you can practice it dry in your home. But, it's not really that useful in a match setting and adds quite a bit of risk to it. There are new guys that can't even safely navigate the current course of fire and rules set!

And something else to think about... how often do you think this happens in a self-defense/combat situation? I asked Frank Proctor this question and he's served 3 tours in Iraq and 3 tours in Afghanistan, doing the scary stuff. He said it's never happened to him and he doesn't know anyone that it's happened to. Maybe it's there but it's super rare.